Keysight (Agilent) 53150A Programmers Guide

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Programming Guide

HP 53150A/151A/152A Microwave Frequency Counter

Programming Guide

This guide describes how to program the HP 53150A, 53151A, and 53152A Microwave Frequency Counters. The information in this guide applies to instruments having the number prefix listed below, unless accompanied by a “Manual Updating Changes” package indicating otherwise.

SERIAL PREFIX NUMBER: 3735A and above (53150A)

3736A and above (53151A) 3737A and above (53152A)

HP 53150A/151A/152A Microwave Frequency Counter



WARNING

CAUTION

WARNING

Reproduction, adaptation, or translations without prior written permission is prohibited, except as allowed under the copyright laws.

Printed: November 1997 Printed in USA

Manual part number 53150-90002

Certification and Warrant

Certification

Hewlett-Packard Company certifies that this product met its published specification at the time of shipment from the factory. Hewlett-Packard further certifies that its calibration measurements are traceable to the United States National Institute of Standards and Technology (formerly National Bureau of Standards), to the extent allowed by the Institute’s calibration facility, and to the calibration facilities of other International Standards Organization members.

Warrant

HP warrants HP hardware, accessories and supplies against defects in materials and workmanship for a period of one year from date of shipment. If HP receives notice of such defects during the warranty period, HP will, at its option, either repair or replace products which prove to be defective. Replacement products may be either new or like-new.

HP warrants that HP software will not fail to execute its programming instructions, for the period specified above, due to defects in material and workmanship when properly installed and used. If HP receives notice of such defects during the warranty period, HP will replace software media which does not execute its programming instructions due to such defects.

For detailed warranty information, see back matter.

Considerations

Safet General

This product and related documentation must be reviewed for familiarization with this safety markings and instructions before operation.

Before Cleaning

Disconnect the product from operating power before cleaning.

Warning S Be Used In This Book

Instruction manual symbol; the product will be marked with this symbol when it is necessary for the user to refer to the instruction manual.

Indicates hazardous voltages.

Indicates earth (ground) terminal.

Indicates terminal is connected to chassis when such connection is not apparent.

Indicates Alternating current.

Indicates Direct current.

mbols That May

Considerations

Safet (contd)

BODILY INJURY OR DEATH MAY RESULT FROM FAILURE TO HEED A WARNING. DO NOT PROCEED BEYOND A WARNING UNTIL THE INDICATED CONDITIONS ARE FULLY UNDERSTOOD AND MET .

Damage to equipment, or incorrect measurement data, may result from failure to heed a caution. Do not proceed beyond a until the indic ated conditio ns are fully understood and met.

Earth Ground

Safet

An uninterruptible safety earth ground must be maintaine d from the mains power source to the product’s ground circuitry.

WHEN MEASURING POWER LINE SIGNALS, BE EXTREMELY CAREFUL AND ALWAYS USE A STEP-DOWN ISOLATION TRANSFORMER WHICH OUTPUT IS COMPATIBLE WITH THE INPUT MEASUREMENT CAPABILITIES OF THIS PRODUCT. THIS PRODUCT’S FRONT AND REAR PANELS ARE TYPCIALLY AT EARTH GROUND.

TO MEASURE AC POWER LINE SIGNALS WITHOUT AN ISOLATION TRANSFORMER.

For additional safety and acoustic noise information, see back matter.

CAUTION

THUS, NEVER TRY

Hewlett-Packard Company 8.NC.NL.A.11.03.97.R1.P.CW1C3NC Santa Clara Divisio n 5301 Stevens Creek Boulevard Santa Clara, California 95052-8059

1 Before You Start ...

Introduction 1-2 Getting Started 1-3 How to Use This Guide 1-3

New Users 1-4 Experienced Programmers 1-5 Applications 1-5

Programming Guide Contents 1-6 Assumptions 1-7 Related Documentation 1-8

2 Command Summar

Introduction 2-2

Chapter Summary 2-2

Front Panel to SCPI Command Map 2-3 HP 53150A/151A/152A Command Summary 2-8

SCPI Conformance Information 2-8 IEEE 488.2 Common Commands 2-9 HP 53150A/151A/152A SCPI Subsystem Commands 2-12 Std/New Column 2-12 Parameter Form Column 2-12

*RST Response 2-19

3 Programming Your Counter

for Remote Operation

Introduction 3-2

Chapter Summary 3-3 Where to Find Some Specific Information 3-4 Programming Examples 3-4

Programming Guide v

Contents

Connecting the Counter to a Computer 3-5

To Connect With the HP-IB 3-5 IEEE 488.1 Interface Capabilities 3-6 To Connect With the RS-232 Serial Interface 3-7 Remote/Local Operation 3-11

Overview of Command Types and Formats 3-12

Common Command Format 3-12 SCPI Command and Query Format 3-12

Elements of SCPI Commands 3-13

Subsystem Command Syntax 3-13 Common Command Syntax 3-13 Abbreviated Commands 3-14 Keyword Separator 3-14 Optional Keyword 3-14 Parameter Types 3-16 Parameter Separator 3-17 Query Parameters 3-17 Suffixes 3-17 Command Terminator 3-18

Using Multiple Commands 3-19

Program Messages 3-19 Program Message Syntax 3-19

Overview of Response Message Formats 3-21

Response Messages 3-21 Response Message Syntax 3-21 Response Message Data Types 3-23

Status Reporting 3 -25

Status Byte Register and Service Request Enable Register 3-27

Standard Event Status Register Group 3-30 The Operation and Questionable Data Status Register

Groups 3-33

vi Programming Guide

Contents

Programming the Counter for Status Reporting 3-41

Determining the Condition of the Counter 3-41 Resetting the Counter and Clearing

the Remote Interface—Exa mple 1 3-42 Using the Standard Event Status Register to

Trap an Incorrect Command—Example 2 3-42 Using the Operation Status Register to Alert the Computer

When Measuring has Completed—Example 3 3-43

Programming the Counter to Display Results 3-46

Configuring the Counter's Display 3-46

Commands for Displaying Results 3-47

Command for Displaying Raw Results 3-47 Commands for Displaying Relative Results 3-47 Commands for Enabling and Disabling the Display 3-47

Programming the Counter to Synchronize Measurements 3-48

Synchronizing Measurement Completion 3-48 Resetting the Counter and Clearing the Inte rface 3-48 Using the *WAI Command 3-49 Using the *OPC? Command 3-49 Using the *OPC Command to Assert SRQ 3-50

Writing SCPI Programs 3-52

Programming Guide vii

Contents

Programming Examples 3-54

Using HP BASIC 3-54 Using C 3-55 List of the Programming Examples 3-55 Making a Frequency Measurement (HP BASIC) 3-56 Making a Frequency Measurement (QuickBASIC) 3-57 Making a Frequency Measurement (C) 3-58

4 Command Reference

Introduction 4-2 :ABORt Command 4-4 :DISPlay Subsystem 4-5 Group Execute Trigger

(GET) 4-7 :INITiate Subsystem 4 -8 :INPut Sub s ys tem 4-9 :MEASure Subsystem 4-10

Measurement Instructions (:CONFigure, :FETCh, :MEASure, :READ) 4-10

Descriptions of the Measurement Functions 4-16 How to Use the Measurement Instruction Commands 4-

:MEMory Subsystem 4-20 [:SENSe] Subsystem 4-22 [:SENSe]:FUNCtion Subtree 4-27

[:SENSe]:POWer Subtree 4-29 [:SENSe]:ROSCillator Subtree 4-30

:STATus Subsystem 4-31

:STATus:OPERation Subtree 4-31 :STATus:QUEStionable Subtree 4-36

:SYSTem Sub sy s te m 4-39

:SYSTem:COMMunicate Subtree 4-39

viii Programming Guide

Contents

:TRIGger Subsystem 4-43 Common Commands 4-44

*CLS (Clear Status Command) 4-45 *DDT (Define Device Trigger Command) *DDT? (Define Device Trigger Query) 4-46 *ESE (Standard Event Status Enable Command) *ESE? (Standard Event Status Enable Query) 4-47 *ESR? (Event Status Register Query) 4-49 *IDN? (Identification Query) 4-50 *IST? (Instrument Status) 4-50 *OPC (Operation Complete Command) 4-51 *OPC? (Operation Complete Query) 4-51 *PRE (Parallel Poll Enable Register) *PRE? (Parallel Poll Enable Register Query) 4-52 *RCL (Recall Command) 4-52 *RST (Reset Command) 4-53 *SAV (Save Command) 4-54 *SRE (Service Request Enable Command) *SRE? (Service Request Enable Query) 4-55 *TRG (Trigger Command) 4-58 *TST? (Self-Test Query) 4-59 *WAI (Wait-to-Continue Command) 4-61

5Errors

Introduction 5-2 Reading an Error 5-3 Error Queue 5-4 Error Types 5-5

No Error 5-5 Command Error 5-6 Execution Error 5-6 Device- or Counter-Specific Error 5-7 Query Error 5-7 Error List 5-7

Programming Guide ix

Contents

x Programming Guide

Before You Start ...

Chapter 1 Before You Start ...

Introduction

This programming guide contains programming information for the HP 53150A, 53151A, and 53152A Microwave Frequency Counters.

This guide assumes you are familiar with the front-panel operation of the Counter. See the information about front-panel operation. You should use this programming guide together with the operating guide. Knowing how to control the Counter from the front panel and understanding the measurements you want to perform makes the programming task much easier. The operating guide provides explanations and procedures for all of the Counter's measurement functions and contains the specifications for the Counter.

By sending Standard Commands for Programmable Instruments (SCPI) commands, you can remotely operate many of the Counter's front-panel functions via the Hewlett-Packard Interface Bus (HP-IB) or the RS-232 serial interface. These programming commands conform to the

Commands for Programmable Instruments (SCPI) Standard Version

1992.0

instruments over the Hewlett-Packard Interface Bus (HP-IB) or the RS-232 serial interface. However, it does standardize the structure and content of an instrument's command set to reflect the best programming practices developed by people using HP-IB. It also establishes standard command mnemonics for similar functions in all of the instruments that conform to the SCPI standard.

. The SCPI standard does not completely redefine how to program

HP 53150A/151A/152A Operating Guide

for detailed

Standard

If you have programmed any HP instruments that have been released over the last few years, you ha ve probably se en a general trend t oward the techniques specified in the SCPI standard. For example, several instruments are already using a hierarchy of commands that is similar to the command structure defined by the SCPI standard.

1-2 Programming Guide

Chapter 1 Before You Start ...

Getting Started

NOTE

Before attempting to program the Counter, take some time to familiarize yourself with the content of this guide. The remainder of this chapter contains the following information:

• An explanation of how you should use the programming guide based on your experience programming instruments and your testing requirements.

• A description of the guide contents.

• A statement of assumptions that are made in the guide.

• A list of related documentation.

How to Use This Guide

How you use this guide depends upon how much you already know about programming instruments and how complex your measurement requirements are. Let's start by establishing your programming background and then discuss the type of mea surements you want to perform.

With two minor exceptions, the only differen ce between programming the Counter using the HP-IB interface and the RS-232 serial interface is the manner in which you connect the Counter to the computer. These exceptions are:

1. The Counter sends a command prompt over the RS-232 interface (but not the HP-IB) after receiving and executing each command.

2. When an error is detected ( during the Self-Test or during o peration), the Counter automatically sends an error message (or messages) over the RS-232 interface (error messages must be requested over the HP-IB). For additional information on error messages, see Appendix B of the

HP 3150A/151A/152A Operating Guide

Programming Guide 1-3

Chapter 1 Before You Start ...

How to Use This Guide

New Users

What You Should Un de rs t a nd

As a new user, you must have some understanding of a high-level language, such as BASIC or C, before you can use the command set defined in this guide to control the Counter. (In Chapter 3, “Programming Your Counter for Remote Operation,” there are programming examples provided in HP BASIC, Microsoft QuickBASIC, and Borland Turbo C.) However, whatever language you use, the command strings that control the Counter remain the same.

Learning to Program the Co un te r

To learn how to program the Counter, perform the following:

• Scan the summary tables in Chapter 2, “Command Summary,” to get a feeling for the number and structure of commands available to you.

• Read and study map drawings in the s ection t itled “F ront Panel to SCPI Command Map” in Chapter 2.

• Read Chapter 3, “Programming Your Counter for Remote Operation,” for an overview of SCPI concepts as they relate to the HP 53150A, 53151A, and 53152A Frequency Counters. Look at the flowcharts, which illustrate some of the decisions you must make when programming the Counter.

• Read the section at the end of Chapter 3 titled “Programming Examples.”

• Modify some of the programming examples to select speci f ic measurement functions. If the programs work, consider yourself an experienced programmer and use Chapter 4, “Command Reference,” as a reference for detailed information of all the Counter's SCPI commands.

1-4 Programming Guide

Chapter 1 Before You Start ...

How to Use This Guide

Experienced Programmers

If you have programmed other HP-IB instruments, you are probably familiar with many of the concepts and techniques discussed in this guide. Using the SCPI commands is also very similar to using the earlier HP-IB commands. The main difference between the two command sets is the hierarchy of the subsystem commands. (However, this type of structure has previously been used on other instruments.)

Because the SCPI command set and some of the status reporting techniques are new, we advise you to use the following sequence to learn the Counter programming requirements:

• Look over the steps for a new user, and perform any that you think are applicable to your current level of knowledge. In particular, look at the measurement techniques and examples provided in Chapter 3, “Programming Your Counter for Remote Operation.”

• Review the summary tables in Chapter 2, “Command Summary.” If this chapter contains sufficient information to get you started, write some test programs to explore the Counter's capabilities. If you need additional information on any command, refer to the applicable command description in Chapter 4, “Command Reference .”

• Review the remaining information in this guide to determine what is applicable to your programming requirements.

If you need more information than is contained in this guide, see the section in this chapter titled “Related Documentation.”

Applications

After you have read the appropriate information and written some measurement programs, you may want to expand the scope of your applications. The following two techniques are explained in detail:

• If you are going to write interrupt-driven programs (or if you just want to determine the status of the Counter), read the sect ion titled “Status Reporting” in Chapter 3.

• If you are going to write programs to transfer data between the Counter and an external computer, read the section titled “Overview of Response Message Formats” in Chapter 3.

Programming Guide 1-5

Chapter 1 Before You Start ...

Programming Guide Contents

The following information is contained in this guide:

• Table of Contents

• Chapter 1 (this chapter),“Before You Start ...,” is a preface that introduces you to the programming guide.

• Chapter 2, “Command Summary,” is a quick reference that summarizes the Counter's programming commands. It provides you with front-panel to SCPI command maps, SCPI conformance information, and command-summary tables.

• Chapter 3, “Programming Your Counter for Remote Operation,” describes how to connect and set up the Counter for remote operation, briefly explains the SCPI elements and formats, describes status reporting, describes how to write programs, and provides programming examples for each of the main tasks that you want the Counter to perform.

• Chapter 4, “Command Reference,” is a command dictionary that describes the SCPI subsystems and IEEE 488.2 Common commands.

• Chapter 5, “Errors,” lists all of the error messages the Counter generates and the cause(s) for each error.

•Index

1-6 Programming Guide

Chapter 1 Before You Start ...

Assumptions

This guide assumes the Counter is correctly installed and interfaced to an external computer. If it is not, and you intend to use the HP-IB, see the IEEE HP-IB Interconnection information in

Tutorial Description of the Hewlett-Packard Interface Bus, 1987.

section in this chapter titled “Related Documentation” for ordering information.) If you intend to use the RS-232 serial interface, see the section in Chapter 3 titled “To Connect With the RS-232 Serial Interface.”

As previously mentioned, this guide also assumes you are familiar with the front-panel opera tion of th e Counte r . See th e

Operating Guide

Knowing how to control the Counter from the front panel and understanding the measurements yo u need to perform makes the programming task much easier.

for detailed information about front-panel operation.

Hewlett-Packard Company,

(See the

HP 53150A/151A/152A

Programming Guide 1-7

Chapter 1 Before You Start ...

Introduction

This chapter is a quick reference that summarizes the Counter's programming commands.

Chapter Summary

Front Panel to SCPI Command Map

•

HP 53150A/151A/152A Command Summary

•

SCPI Conformance Information pg. 2-8

–

IEEE 488.2 Common Commands pg. 2-9

–

HP 53150A/151A/152A SCPI Subsystem Commands pg. 2-12

–

*RST Response

•

pg. 2-3

pg. 2-8

pg. 2-19

1 The section titled “Front Panel to SCPI Command Map” provides maps that show the front-panel keys and their corresponding (or related) SCPI commands.

2 The section titled “HP 53150A/151A/152A Command Summary” lists the IEEE 488.2 Common Commands and SCPI Subsystem commands in Table 2-1 and Table 2-2, respectively.

3 The section titled “*RST Response,” lists the states of all of the commands that are affected by the *RST command in Table 2-3. This section also lists commands that are unaffected by *RST in Table 2-4.

2-2 Programming Guide

Chapter 2 Command Summary

Front Panel to SCPI Command Map

Figures 2-1 and 2-2 are command maps that shows the relationships between the front-panel keys and the SCPI commands. This map should help you to identify commands, if you are already familiar with the front panel.

NOTE

Some SCPI S

[ ] An element inside brackets is optional. Note, the

1 | 2 Means use either 1 or 2. <numeric_value> Means enter a number. SENSe Means you

When you see quotation marks in a command’s parameter (shown in the Parameter Form column in Table 2-2), you must send the quotation marks with the command. Refer to the section titled “Using HP BASIC” on page 3-54 of this guide for details on how to use double quotes or single quotes to enclose the string parameter of a command.

ntax Conventions:

brackets are be sent to the Counter.

the entire word. The lo wer case letters are opt ional . For example, SENS and SENSE are both valid. However, SEN is not valid. (Note SENSe is used here as an example, but this conven t io n applie s to all SCP I commands.)

part of the command and should

not

use either all the upper case letters or

must

not

Programming Guide 2-3

Chapter 2 Command Summary

Front Panel to SCPI Command Map

Shift + Freq Offset Shift + Pwr Offset

Rate Avg

MODIFY

Rate

Clear

On/Off

Pwr Offset

Avg

+/-

HPIB Resol

Enter

Reset/ Local

Shift

Freq Offset

Reset/Local

Shift + HPIB

Resolution

Chan Select

Freq Offset On/Off

FREQ

Chan Select

Rel Freq Offset

On/Off

Gate

Shift + On/Off

POWER

Channel 2

dBm/ W Display

Power

Rel Pwr Offset

On/Off

Display Power

Power Offset On/Off

Figure 2-1. Front Panel Control to SCPI Command Map (Part 1 of 2)

2-4 Programming Guide

Chapter 2 Command Summary

Front Panel to SCPI Command Map

1 INITitiate[:IMMediate] 2 TRIGger[:SEQuence]:HOLDoff 3 [SENSe]:FREQuency:OFFSet 4 [SENSe]:POWer:AC:REFerence 5 [SENSe]:AVERage:COUNt 6 [SENSe]:AVERage:STATe 7 SYSTem:COMMunicate:GPIB:ADDRess 8 [SENSe]:FREQuency:RESolution

9 DISPlay:BACKground[:STATe] 10 [SENSe]:FUNCtion 11 [SENSe]:POWer:AC:REFerence:STATe 12 [SENSe]:FREQuency:OFFSet:STATe 13 [SENSe]:FUNCtion

Figure 2-1. Front Panel Control to SCPI Command Map (Part 2 of 2)

Programming Guide 2-5

Chapter 2 Command Summary

Front Panel to SCPI Command Map

Shift + Menu REF OSC

SAVE

RECALL

CH1 LPF

BAUD

PRESET

Instrument ID

OP HRS

BATT VOLTAGE

DO SELF TEST

PWR CORR

Reset/ Local

Shift

Freq Offset

Rate

On/Off

Clear

Figure 2-2. Front Panel Menu to SCPI Command Map (Part 1 of 2)

2-6 Programming Guide

Chapter 2 Command Summary

Front Panel to SCPI Command Map

1 [:SENSe]:ROSCillator:SOURce

2 *SAV

3 *RCL

4 :INPut:FILTer[:LPASs][:STATe]

5 [:SENSe]:FILTer:FM:AUTO

6 :SYSTem:COMMunicate:SERial[:RECeive]:BAUD

7 *RST

8 *IDN?

9 See Service Manual 10 See Service Manual 11 *TST? 12 MEMory:CLEar[:NAME]

MEMory:DATA [:SENSe]:CORRection:CSET:SELect [:SENSe]:CORRection:CSET:STATe

Figure 2-2. Front Panel Menu to SCPI Command Map (Part 2 of 2)

Programming Guide 2-7

Chapter 2 Command Summary

HP 53150A/151A/152A Command Summary

This section summarizes both the IEEE 488.2 Common and HP 53150A/151A/152A Standard Commands for Programmable Instruments (SCPI) commands in tabular format. IEEE 488.2 Common Commands are listed first, followed by SCPI commands.

SCPI Conformance Information

The SCPI commands used in the HP 53150A/151A/152A Counters are in

conformance with the SCPI Standard Version 1995.0. The SCPI command set consists of the followi n g:

• Common Commands as defined in IEEE 488.2-1987—listed and summarized in Table 2-1.

• SCPI Subsystem commands as confirmed (and listed) in the SCPI Standard—the commands defined in Table 2-2 as “Std.”

• SCPI Subsystem commands designed for the instrument in conformance with SCPI standards but not yet listed in the SCPI Standard—the commands defined in Table 2-2 as “New.”

• Details of all HP 53150A/151A/152A commands can be found in Chapter 4, “Command Reference.”

Information on the SCPI commands format, syntax, parameter, and response types is provided in Chapter 3, “Programming Your Counter for Remote Operation.”

2-8 Programming Guide

Chapter 2 Command Summary

HP 53150A/151A/152A Command Summary

IEEE 488.2 Common Commands

The Common Commands are general-purpose commands that are common to all instruments (as defined in IEEE 488.2). Common Commands are easy to recognize because they all begin with an “*” (for example, *RST, *IDN?, *OPC). These commands are generally not related to measurement configuration. They are used for functions like resetting the instrument, identification, or synchronization.

Table 2-1 lists the IEEE 488.2 Common Commands supported by the HP 53150A/151A/152A in alphabetical order by mnemonic, name, and function. More information concerning the operation of IEEE 488.2 status-reporting commands and structure can be found i n the “Status Reporting” section of Chapter 3. Standard explanations of the IEEE 488.2 Common Commands can be found in the ANSI/IEEE Std. 488.2-1987, IEEE Standard Codes, Formats, Protocols, and Common Commands document.

Programming Guide 2-9

Chapter 2 Command Summary

HP 53150A/151A/152A Command Summary

Table 2-1. IEEE 488.2 Common Commands

Mnemonic Command Name Function

*CLS Clear Status Clears all event status registers summarized in the

status byte and empt ies the Error Queue.

*DDT <arbitrary block> Defi ne Device Trigger

Command

*DDT? Define Device Trigger

Query

*ESE <NRf> Standard Event Statu s

Enable

*ESE? Standard Event Statu s

*ESR? Event Status Register

*IDN? Identification Query Queries the Counter identification. *IST? Instrument Status

*OPC Operation Complete Causes Counter to set the operation compl ete bit in

*OPC? Operation Complete

*PRE <NRf> Parallel Poll Enable

*PRE? Parallel Poll Enable

*RCL <NRf> Recall Restores the state of the Counter’s user settings from

*RST Reset Resets the Counter to a known state, as defined in

*SAV <NRf> Save Stores the current state of the Counter’s user settings

*SRE <NRf> Service Request Enable Sets the Service Request Enable register.

Enable Query

Query

Defines which command is executed when the Counter receives a GET or *TRG command.

Queries which command is executed when the Counter receives a GET or *TRG command.

Sets the Standard Event Status Enable Register.

Queries the Standard Event Status Enable Register.

Queries and then clears the Standard Event Status Register.

Queries the current state of the parallel poll response (Instrument Status).

the Standard Event Status Register when all pending operations (see Note at the end of table) are finished.

Places an ASCII "1" in the Output Queue when all pending operation s (see Note at the end of table) are completed.

Sets the value of the Parallel Poll Enable register.

Queries the value of the Parallel Poll Enable register.

a copy stored in local no n-vol atile me mory (0 throug h 9 are valid memory registers).

this manual.

in local non-vo latile memory (0 through 9 are valid memory registers).

2-10 Programming Guide

+ 156 hidden pages

Keysight (Agilent) 53150A Programmers Guide

Specifications and Main Features

Frequently Asked Questions

User Manual

Contents

Introduction

Getting Started

How to Use This Guide

New Users

What You Should Un de rs t a nd

Learning to Program the Co un te r

Experienced Programmers

Applications

Programming Guide Contents

Assumptions

Related Documentation

Introduction

Chapter Summary

Front Panel to SCPI Command Map

HP 53150A/151A/152A Command Summary

SCPI Conformance Information

IEEE 488.2 Common Commands